Runtime Interface Reflection: type_description_interfaces_utils

[methylDragon]

This PR is part of the runtime interface reflection subscription feature of REP-2011: https://github.com/ros2/ros2/issues/1374

Description

This PR adds a utilities library for manipulating and constructing the C structs generated by type_description_interfaces, including:

• Handy print functions
• Hash map construction
• Sorting and pruning of referenced types (to prep them for hashing)
• Checking of type validity
• Appending fields and referenced type descriptions
• Creating TypeDescriptions from referenced type descriptions (description subsetting)

I also pre-generate the type_description_interfaces sources and headers to create a new package (type_description_interfaces_static) to remove a dependency cycle downstream. (That's why there are so many lines.)

I haven't implemented tests yet, so some memory management issues/segfaults are expected. I'm working on it, but I am wary of spending too much time getting 100% coverage because we're trying to meet the deadline for feature freeze...

I've implemented a bunch of tests and I'm fairly confident that most of the core functionalities work as expected now, so I'm going to mark the PR as ready to review.

Asan runs green too!

clear && \
colcon build --packages-select type_description_interfaces_utils \
  --build-base=build-asan --install-base=install-asan \
  --cmake-args -DOSRF_TESTING_TOOLS_CPP_DISABLE_MEMORY_TOOLS=ON \
               -DINSTALL_EXAMPLES=OFF -DSECURITY=ON --no-warn-unused-cli \
               -DCMAKE_BUILD_TYPE=Debug \
  --mixin asan-gcc && \
colcon test --build-base=build-asan --install-base=install-asan \
  --event-handlers sanitizer_report+ --packages-select type_description_interfaces_utils

There are some less important tests waiting to be written (printing), and some tests that are already implicitly covered by other tests (but are not explicit yet.)

TODO

• [ ] More minor tests
• [ ] 100% docstring coverage

Open Questions

• This only operates on the C version of the type_description_interfaces struct... Do I need to write a C++ version? (Is there a way to convert between the two versions of the message, or are they otherwise interchangeable?)
  • Perhaps that C++ utils library would just have a conversion function, since we know the layout of the struct already???
• Should this be type_description_interfaces_utils_c instead? :grimacing:

[methylDragon]

Closing this in favor of https://github.com/ros2/rosidl/pull/728